Is a subset of a problem solution, used to recreate complete solution considered a heuristic?
Whether or not a label fits any particular instance depends on what you're using the label for. If something specific is riding on whether this approach is a 'heuristic' or not, that context is important.

But I wouldn't call this a heuristic, because I think of that as a shortcut for solving a problem, not either storing a solution or reformulating the problem (which is how I'd think of this).